This invention pertains to hermetic rotary compressors for compressing refrigerant in refrigeration systems such as air conditioners, refrigerators, and the like. In particular, the invention relates to the manner of sealing the suction tube to the cylinder in a rotary hermetic compressor.
In general, prior art hermetic rotary compressors comprise a housing which is hermetically sealed. Located within the housing are an electric motor and a compressor mechanism. The electric motor is connected to a crankshaft which has an eccentric portion thereon. The eccentric portion of the crankshaft is located within a bore of the compressor cylinder. A roller located within the bore is mounted on the eccentric portion of the crankshaft and is driven thereby. The roller cooperates with a sliding vane to compress refrigerant within the bore of the cylinder.
Rotary hermetic compressors of the type herein disclosed generally have a pressurized or high side sealed housing. The compressor is connected into a refrigeration circuit by means of suction and discharge tubes. In the prior art compressors the motor stator may be secured to the interior wall of the housing by shrink fitting and the compressor cylinder is generally welded to the housing. A motor rotor is journalled in a bearing and drives the crankshaft. The suction tube extends through the housing and is sealingly connected thereto. The end of the suction tube which extends into the housing is connected to the cylinder and conducts low pressure refrigerant directly to the cylinder bore for compression therein. The connection of the suction tube to the cylinder is usually made by press fitting or swedging the tube into an aperture in the cylinder wall. To that end, the suction tube outside diameter is made larger than the inside diameter of the cylinder aperture so that a good friction fit can be achieved.
The tolerances to which the cylinder, roller and vane must be manufactured are generally very exacting, such as ten thousandths of an inch. The reason for such very tight tolerances is that leakage of refrigerant in compressors must be minimized in order to achieve acceptable efficiencies of the compressor pumps. Since the assembly operations of welding the cylinder to the housing and pressing or swedging the suction tube into the cylinder aperture tend to distort the cylinder, thereby causing vane slot distortion and misalignment between the cylinder and the bearing, the prior art cylinders have generally been designed with a relatively large axial dimension so as to be of relatively heavy construction. By providing a thick, heavily constructed cylinder the press fitted suction tube is surrounded by sufficient cylinder material so that distortion is minimized, vane slot geometry and alignment of the bearings are preserved, and close tolerances are maintained. If distortion were not minimized and the dimensional tolerances could not be held during the welding and swedging operations, leakage in the compressor would become excessive.
In one prior art compressor having a low side housing the sealed connection of the suction tube to the suction muffler was made by means of an O ring. In this application of an O ring to a compressor structure the O ring did not provide a sealing connection between compressor areas of high pressure differentials such as the suction and discharge gas areas. Furthermore, this prior art compressor was of the reciprocating rather than the rotary variety so that there was no need for a thin cylinder to which the suction tube had to be sealingly connected and in which a large pressure drop existed across the sealed connection.
The prior art solution to the problem of providing a suitable sealed suction tube connection to the cylinder in a high side rotary compressor by using a thick cylinder and having the suction tube pressed therein has the disadvantage that it tends to increase the length of the refrigerant leakage paths and heat transfer surface thereby tending to decrease the efficiency of the compressor. During operation of the compressor there are areas of various pressure levels within the compressor. For instance, the bore of the compressor cylinder has both an inlet portion at suction pressure and a high pressure portion wherein the gas is compressed. Furthermore, the compressor housing itself is at high pressure because compressed refrigerant is expelled from the cylinder bore directly into the housing. As pointed out above, it is important to keep leakage of refrigerant from high pressure areas to low pressure areas to a minimum, since such leaked refrigerant represents lost work and reduces the efficiency of the compressor. Therefore, it is important that the lengths of the borders dividing low and high pressure areas are made as small as possible. It can be readily understood that the height of the cylinder is a critical dimension affecting leakage since it is directly related to the border length dividing the high and low pressure areas in the compressor cylinder bore. For instance, the length of the tip of the sliding vane which contacts the roller and the cracks between the vane and vane slot form a border dividing the high and low pressure cylinder bore areas. By using a thin cylinder this critical dimension can be kept small and the refrigerant leakage past the vane as well as other borders can be reduced.
An added disadvantage of the prior art thick cylinder construction is that the weight of the compressor is increased which is undesirable since the compressors are used in household appliances which are preferably of lightweight construction. Accordingly, a thin cylinder is desired.
Another disadvantage of prior art compressor structures has been that special shock absorbing structures had to be provided for the suction tube end extending into the compressor housing and located between the housing and the cylinder. Pressures in compressor housings tend to fluctuate and tend to rise as the compressor is shut down. Such pressure variations cause flexing of the housing. Since prior art suction tubes were secured to both the cylinder and the housing, the flexing of the housing due to varying pressures had to be accommodated to prevent rupturing of the suction tube seals with the housing and the cylinder. Thus, prior art structures provided shock tubes and other means to accommodate the stresses on the suction tube. It is, therefore, desired to accommodate the stresses on the suction tube in a simple manner while ensuring proper seals between the suction tube, the housing and cylinder.
The heavy construction of the cylinders of prior art compressors tended not only to increase the length of the leakage paths but also tended to increase the surface area available for heat transfer to incoming suction gas. Such heat transfer is undesirable and tends to decrease the efficiency of the compressor. It is, therefore, desirable that the heat transfer surface areas are minimized in order to optimize the efficiency of the compressor.
Another disadvantage of prior art rotary hermetic compressors is that in the sealing of the suction tube to the cylinder the use of fittings is necessitated thereby increasing the cost of the compressors due to the cost of parts and the cost of assembling the parts.
One further disadvantage of thick cylinders is that it tends to increase the size of the compressor. Since hermetic compressors are used in articles such as home appliances it is desirable that the size of the compressors is minimized.